1. Field of the Invention
The present invention relates to the field of power converters, such as switched-mode power supply systems or linear regulators meant for supplying a load under a regular fixed voltage. Such converters receive a d.c. voltage from a battery or a rectifying bridge of the a.c. mains voltage associated with a storage capacitor. The present invention more specifically applies to maintenance of the load supply voltage even in case of an abrupt variation of the current therein. For example, the present invention applies to power converters for supplying a microprocessor, the current surge of which may vary, with a relatively high recurrence frequency (from on the order of a few hertz to several kilohertz), between a few mA and 10 or 15 A, or even more.
2. Discussion of the Related Art
The increase in microprocessor performance requires power converters with higher and higher performance with respect to their voltage stability and their rate of response to a variation of the charge. For example, a converter for supplying a microprocessor known under trademark "PENTIUM-PRO" of "Intel" must withstand a current variation from 0.3 A to 10 A in 350 nanoseconds with a voltage accuracy of .+-.5%.
Several conventional solutions are used to improve the response of the converter to such abrupt current variations.
FIG. 1 shows an example of a conventional circuit for supplying a microprocessor. A DC/DC converter 1 receives a supply voltage Ve, for example, +12 volts or +5 volts and provides a voltage Vin to a microprocessor 2. The value of voltage Vin (for example, +2.1 to +3.5) volts is generally set by microprocessor 2 which communicates with converter 1 over a digital link 3. Several chemical storage capacitors C are connected in parallel between supply line Vin and the ground to limit the transient variations of voltage Vin after a variation of the current surged by microprocessor 2. One or several ceramic decoupling capacitors C' are generally connected between a supply terminal S of the microprocessor receiving voltage Vin and the ground.
A disadvantage of this solution is that capacitors of high capacitances, which must further have a very low equivalent series resistance and inductance, are very expensive. A conventional solution such as shown in FIG. 1 typically requires, for the above example of a "PENTIUM-PRO" microprocessor, ten chemical capacitors of 1500.degree. F., each having an equivalent series resistance of 44 m.OMEGA., to reach a capacitance higher than 4000 .mu.F with an equivalent series resistance lower than 5 m.OMEGA. corresponding to the constraints set by the manufacturer. Further, the equivalent series inductance of a capacitor generally is 10 nH.
Another solution, applicable if the power converter is a switched-mode power supply (PWM), is to operate the switched-mode power supply at high switching frequencies. If such a solution requires chemical capacitors of lower capacitance between the converter and the microprocessor, their equivalent series inductance and resistance remain critical as concerns the cost. Further, designing a switched-mode power supply operating at 500 kHz, or even more, requires the use of high performance components, especially to stabilize the feedback loop while taking into account the behavior of the components and the pattern of the printed circuit at such a high frequency.